Drinking water treatment typically involves chlorination of municipal water (e.g., via addition of Cl<sub>2</sub> or NaOCl). Bromide is also present at detectable levels in most drinking water sources. Bromide can be oxidized by chlorine into electrophilic bromine species (e.g., HOBr). Current methods for quantifying residual chlorine in aqueous solutions cannot distinguish between chlorine and bromine. The purpose of this research is to develop a selective method for quantification of chlorine and bromine using aromatic compounds as halogen trapping agents: 1,3,5-trimethoxybenzene (TMB), 1,4-dimethoxybenzene (DMB), and 2,6-dimethylanisole (DMA). Each of these trapping agents reacts readily with aqueous chlorine and bromine, presumably via electrophilic aromatic substitution. In the presence of excess trapping agent, these reactions are anticipated to yield one monochlorinated and one monobrominated product, with the concentration of the halogenated product equaling the initial concentration of the respective halogen. We evaluated the effects of pH, initial TMB concentration, and initial chlorine/bromine concentration in order to determine optimal conditions for quantifying chlorine and bromine. Reactors were analyzed using high-performance liquid chromatography (HPLC) with UV-vis detection. Results indicate that the halogen trapping agents can selectively quantify chlorine and bromine at pH values typical of raw and treated drinking water (pH = 6 – 8). When TMB was used as a halogen trapping agent, percent recoveries of chlorine and bromine were generally not significantly different than 100%. A TMB-to-halogen molar ratio of at least 7:1 was required for accurate quantification, though optimum percent recovery was achieved with a ratio of approximately 40:1. In addition to HPLC, all halogen trapping agents listed above and their halogenated products can also be analyzed via gas chromatography/mass spectrometry. This method can be applied in order to quantify concentrations of residual free chlorine in chlorinated pool water, drinking water, and other chlorinated aqueous systems.<br/>

Selective quantification of chlorine and bromine in water using halogen trapping agents

253rd National Meeting (2017)

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